skip to main content


Title: Patterning of Lyotropic Chromonic Liquid Crystals by Photoalignment with Photonic Metamasks

Controlling supramolecular self‐assembly in water‐based solutions is an important problem of interdisciplinary character that impacts the development of many functional materials and systems. Significant progress in aqueous self‐assembly and templating has been demonstrated by using lyotropic chromonic liquid crystals (LCLCs) as these materials show spontaneous orientational order caused by unidirectional stacking of plank‐like molecules into elongated aggregates. In this work, it is demonstrated that the alignment direction of chromonic assemblies can be patterned into complex spatially‐varying structures with very high micrometer‐scale precision. The approach uses photoalignment with light beams that exhibit a spatially‐varying direction of light polarization. The state of polarization is imprinted into a layer of photosensitive dye that is protected against dissolution into the LCLC by a liquid crystalline polymer layer. The demonstrated level of control over the spatial orientation of LCLC opens opportunities for engineering materials and devices for optical and biological applications.

 
more » « less
NSF-PAR ID:
10033071
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Advanced Materials
Volume:
29
Issue:
21
ISSN:
0935-9648
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Liquid crystals offer a dynamic platform for developing advanced photonics and soft actuation systems due to their unique and facile tunability and reconfigurability. Achieving precise spatial patterning of the liquid crystal alignment is critical to developing electro‐optical devices, programmable origami, directed colloidal assembly, and controlling active matter. Here, a simple method is demonstrated to achieve continuous 3D control of the directions of liquid crystal mesogens using a two‐step photo‐exposure process. In the first step, polarized light sets the orientation in the plane of confining substrates; the second step uses unpolarized light of a prescribed dose to set the out‐of‐plane orientation. The method enables smoothly varying orientational patterns with sub‐micrometer precision. As a demonstration, the setup is used to create gradient‐index lenses with parabolic refractive index profiles that remain stable without external electric fields. The lenses' focal length and sensitivity to light polarization are characterized through experimental and numerical methods. The findings pave the way for developing next‐generation photonic devices and actuated materials, with potential applications in molecular self‐assembly, re‐configurable optics, and responsive matter.

     
    more » « less
  2. null (Ed.)
    Approaches to control the microstructure of hydrogels enable the control of cell–material interactions and the design of stimuli-responsive materials. We report a versatile approach for the synthesis of anisotropic polyacrylamide hydrogels using lyotropic chromonic liquid crystal (LCLC) templating. The orientational order of LCLCs in a mold can be patterned by controlling surface anchoring conditions, which in turn patterns the polymer network. The resulting hydrogels have tunable pore size and mechanical anisotropy. For example, the elastic moduli measured parallel and perpendicular to the LCLC order are 124.9 ± 6.4 kPa and 17.4 ± 1.1 kPa for a single composition. The resulting anisotropic hydrogels also have 30% larger swelling normal to the LCLC orientation than along the LCLC orientation. By patterning the LCLC order, this anisotropic swelling can be used to create 3D hydrogel structures. These anisotropic gels can also be functionalized with extracellular matrix (ECM) proteins and used as compliant substrata for cell culture. As an illustrative example, we show that the patterned hydrogel microstructure can be used to direct the orientation of cultured human corneal fibroblasts. This strategy to make anisotropic hydrogels has potential for enabling patternable tissue scaffolds, soft robotics, or microfluidic devices. 
    more » « less
  3. Abstract

    Research on lyotropic chromonic liquid crystals has grown tremendously from fundamental studies to designing functional materials for applications in biological fields and other technological areas. The majority of the research has centered on utilizing chromonic small molecules predominantly dissolved in aqueous solvents. But these often present processing difficulties and a host of other unattractive features including poor mechanical and chemical stabilities. Mesophase properties of chromonic liquid crystals as characterized using X‐ray diffraction and scattering techniques, spectroscopy and light microscopy are explored. We review potential applications and future perspectives of this subfield where methods of transforming chromonic molecules into functional materials are highlighted. © 2020 Society of Industrial Chemistry

     
    more » « less
  4. Abstract

    The ability to print soft materials into predefined architectures with programmable nanostructures and mechanical properties is a necessary requirement for creating synthetic biomaterials that mimic living tissues. However, the low viscosity of common materials and lack of required mechanical properties in the final product present an obstacle to the use of traditional additive manufacturing approaches. Here, a new liquid‐in‐liquid 3D printing approach is used to successfully fabricate constructs with internal nanostructures using in situ self‐assembly during the extrusion of an aqueous solution containing surfactant and photocurable polymer into a stabilizing polar oil bath. Subsequent photopolymerization preserves the nanostructures created due to surfactant self‐assembly at the immiscible liquid–liquid interface, which is confirmed by small‐angle X‐ray scattering. Mechanical properties of the photopolymerized prints are shown to be tunable based on constituent components of the aqueous solution. The reported 3D printing approach expands the range of low‐viscosity materials that can be used in 3D printing, and enables robust constructs production with internal nanostructures and spatially defined features. The reported approach has broad applications in regenerative medicine by providing a platform to print self‐assembling biomaterials into complex tissue mimics where internal supramolecular structures and their functionality control biological processes, similar to natural extracellular matrices.

     
    more » « less
  5. Lyotropic chromonic liquid crystals (LCLCs) represent aqueous dispersions of organic disk-like molecules that form cylindrical aggregates. Despite the growing interest in these materials, their flow behavior is poorly understood. Here, we explore the effect of shear on dynamic structures of the nematic LCLC, formed by 14 wt% water dispersion of disodium cromoglycate (DSCG). We employ in situ polarizing optical microscopy (POM) and small-angle and wide-angle X-ray scattering (SAXS/WAXS) to obtain independent and complementary information on the director structures over a wide range of shear rates. The DSCG nematic shows a shear-thinning behavior with two shear-thinning regions (Region I at  < 1 s −1 and Region III at  > 10 s −1 ) separated by a pseudo-Newtonian Region II (1 s −1 <  < 10 s −1 ). The material is of a tumbling type. In Region I,  < 1 s −1 , the director realigns along the vorticity axis. An increase of  above 1 s −1 triggers nucleation of disclination loops. The disclinations introduce patches of the director that deviates from the vorticity direction and form a polydomain texture. Extension of the domains along the flow and along the vorticity direction decreases with the increase of the shear rate to 10 s −1 . Above 10 s −1 , the domains begin to elongate along the flow. At  > 100 s −1 , the texture evolves into periodic stripes in which the director is predominantly along the flow with left and right tilts. The period of stripes decreases with an increase of  . The shear-induced transformations are explained by the balance of the elastic and viscous energies. In particular, nucleation of disclinations is associated with an increase of the elastic energy at the walls separating nonsingular domains with different director tilts. The uncovered shear-induced structural effects would be of importance in the further development of LCLC applications. 
    more » « less